The technique of interlacing was developed for cathode ray tube (CRT) display screens. This technique involves dividing one frame into two sets of fields, viz. a top field and a bottom field. Each field includes half of the lines (or row of pixels) required to generate the picture. For example, a first field (a top field) may include the odd pixel rows of the image and a second field (a bottom field) may include the even pixel rows of the image. During each refresh cycle of an interlaced screen, half of the pixel rows are refreshed (either odd rows or even rows), thereby decreasing the amount of data that is processed prior to displaying. As a result, the bandwidth requirements of interlaced display screens are reduced by half as compared to the display screens that refresh each pixel row during each refresh cycle (progressive scan display screens). Additionally, since the number of pixels to be processed is reduced by half, an interlaced display screen can provide twice the refresh rates as compared to the progressive scan display screens, thereby providing better picture quality. Thus, this technique improves picture quality without incurring a bandwidth overhead and reduces cost of display equipments by reducing the bandwidth requirements.
Further, an interlaced display screen may function in a manner in which the top field is refreshed first and thereafter the bottom field is refreshed or vice versa. Since, the two fields are shot at different instances of time, the chronological ordering of the fields (or field order) while being refreshed is important for a smooth rendering of the video. In traditional analog interlaced video, the information related to the field order is included in the encoded video stream. However, due to the convergence in the analog and digital technologies an interlaced analog video may undergo processes such as digital sampling, editing, and so forth before being displayed. As a result of these processes, the field order information is prone to being lost. In the absence of the field order information, the fields may be displayed in an incorrect chronological order. This leads to video jerkiness and hence higher bit rate would be required by the encoder to compress this video sequence. Video jerkiness affects the quality of the video signal received at the user end. Thus, there is a need to correctly detect the field order of a video sequence so that the video may be rendered in the correct chronological order.